The present invention relates to the inspection of components using eddy current technology and, more particularly, to a device for inspecting a component having a complex geometric shape, such as a dovetail slot, gear tooth or the like of a gas turbine engine component or similar workpiece using a multiplicity of eddy current probe or circuit elements formed in an array to provide inspection of a larger surface area in a shorter time than has heretofore been available with a substantially lower probability of missing a flaw or defect.
Eddy current inspection is a commonly used technique for detecting discontinuities or flaws in the surface of components such as the components of a gas turbine engine. Eddy current techniques are based on the principle of electromagnetic induction in which eddy currents are induced within the component under inspection. The eddy currents are induced in the component by alternating magnetic fields created in a coil of an eddy current probe, referred to as a drive coil, when the probe is moved into proximity with the component under inspection. Changes in the flow of eddy currents are caused by the presence of a discontinuity or a crack in the test specimen. The altered eddy currents produce a secondary magnetic field which is received by the eddy current probe coil or by a separate sense coil in the eddy current probe which converts the altered secondary magnetic field to an electrical signal which may be recorded on a strip chart or similar device for analysis. An eddy current machine operator may then detect and size flaws by monitoring and analyzing the recorded signals. Flaws or defects are detected if the electrical signal exceeds a predetermined voltage threshold.
Referring to FIG. 1, a present method of inspecting a component 10, such as a dovetail slot of a rotor, spool or disk of a gas turbine engine, as shown in FIG. 1, uses a single eddy current probe which will typically have two coils connected in a bridge circuit for simultaneous driving and sensing. The single eddy current probe 12 is moved linearly, as indicated by arrow 14 across the interior surface 16 of dovetail slot 18 to scan the surface and detect any flaws or defects present therein. After a complete scan across interior dovetail slot surface 16 in direction 14, the single eddy current probe 12 is indexed or incrementally moved to a next scan location 12' as shown in phantom in FIG. 1. The probe at location 12' is then scanned again across the interior surface 16 of dovetail slot 18. This systematic process of scanning and indexing the single probe 12 is repeated until the entire interior surface 16 of dovetail slot 18 desired to be inspected has been scanned. This single probe/line scan procedure typically requires an extended period of time to substantially completely and adequately inspect the desired surface area even for relatively small dovetail slots and will take even longer as the slot size increases for larger disks and rotors. Additionally, the eddy current probe 12 must be carefully indexed each time so that no area and any small flaws within this area will be missed.